Problem: Tiffany has taken 3 quizzes and her average score so far is 85. If she gets 100, a perfect score, on the remaining 2 quizzes, what will her new average be?
Explanation: If she gets 100 on the remaining quizzes, the sum of her scores will be $3 \cdot 85 + 2 \cdot 100 = 455$ Her overall average will then be $455 \div 5 = 91$.